The invention relates to integrated office communication systems which provide, in addition to conventional telephone services, data communication services and other advanced communication services for users in offices and other working environments.
In present-day office work it is necessary to arrange for employees versatile communication connections capable of transmitting speech, faxes, e-mail and other data, which usually is in digital form. Communication is needed inside an office or sinilar working environment for communication between the employees, communication between different offices of a company which may be located in different cities or even in different countries, and for communication between the office and the "outside world". Here and throughout the text to follow, an "office" means a multi-user environment wherein the users in some way belong together and which is physically located in a relatively small area. There has been a tendency in the field toward integrated systems, in which different forms of transmission can be managed as a whole.
A conventional implementation of such an integrated office communication system comprises a private branch exchange and telephones connected to it with twisted-pair lines in order to provide telephone services, and a separate local area network (LAN) which contains applications for advanced communication services and the intelligence needed to use them. The local area network is connected to the private branch exchange via a telephony server which supports the traditional client/server architecture in which the clients are users' computers connected to the local area network. The telephony server can combine e.g. the office's phone call, data, fax, e-mail and voice mail services. In an integrated system, the users may also manage the telephone services via their computer terminals connected to the local area network. The whole integrated office communication system is connected to a public telephone network via the private branch exchange.
FIG. 1 shows an example of a known integrated office communication system, in which users' telephones TP are connected via wired connections to a private branch exchange PBX connected to a public switched telephone network PSTN, and a local area network LAN is connected to it via a telephony server TS. Servers implementing different applications, such as a database server DBS, voice server VS and an e-mail server EMS, are connected to the local area network, as are the users' computers PC The problem associated with this kind of implementation is that even though a user's telephone TP and computer PC are usually located side by side on the same desk, they must have separate wired connections from the private branch exchange PBX on one hand and from the telephony server TS of the local area network LAN on the other. Building and maintaining two overlapping communication networks is naturally costly.
The problem of overlapping communication networks is made worse by the rapid growth in the number of portable mobile stations utilizing radio communication. Because of mobile work, many office workers need a mobile phone and often also a portable fax and/or a combination of a portable computer and a mobile phone. To make these devices useable also inside buildings, where the structures attenuate radio signals, it has been proposed, for example, that the mobile communication network be supplemented with small base stations covering an office or even a room in an office, which would be connected either directly or via a wired telephone network to the switching systems of the mobile network. That network of small base stations would constitute a third overlapping transmission network in an office, and therefore it is clear that in an advantageous solution, at which the present invention is aimed, an arrangement which supports radio communication devices should be realized by substantially the same means as the rest of the communications in the office.
It is a challenge for the communication systems that more and more work is being done in the small office, home office (SOHO) environment. There, too, there is often a need for advanced office communication services, and it is particularly advantageous if there is a flexible system which can be used both in the office and at home. The present systems, which require overlapping connections for the mobile communication services, ordinary telephone services and fast data transmission services, are rather inflexible as far as working in a small or home office is concerned.
To describe the prior art we will next briefly discuss some solutions related to integrated communication systems. PCT application document WO 94/14291 discloses an arrangement the purpose of which is to simplify and automatize the use of services ordered by phone. The publication discloses an embodiment, wherein a user makes a phone call from a wired telephone to an automatic exchange and indicates with a push-button code that she wants to order a taxi. The number of said wired phone is automatically conveyed to the exchange which checks the location of the phone from a suitable database. Then the exchange checks from an (automatically updated) taxi database which taxi is geographically closest to the caller in question and can provide the desired lift. To update the taxi database and make connections to taxis, each taxi has a mobile station using radio connection. For transmission, the exchange and its auxiliary equipment, such as the unit answering calls, the databases and the base stations maintaining the radio links, are interconnected via a local area network which can transmit voice information in addition to data. Unlike the present invention, the system is not aimed at reducing overlapping communication networks, but its stated intention is to substitute computers for human labour in an exchange conveying taxi services.
EP application document no. 599,632 discloses a wireless local area network the purpose of which is to replace a current wired network (such as Ethernet and Token Ring, both registered trademarks) with a radio network, which in a way constitutes a cellular radio system of its own, intended for data transmission, inside a company. Said application document concentrates mainly on the handling of problems caused by multipath propagation in a wireless local area network and proposes a solution wherein the data transmission time constant of the system, or the inverse of the bit rate, is smaller than the typical delay caused by multipath propagation.
EP application document no. 462,728 discloses an intelligent base station controller which controls at least one base station of a radio-based communication system and which is capable of transmitting calls coming from a certain mobile station via a base station directly to a wired telephone network. The idea of the system is that since a call directed directly to a wired network does not utilize the database services of a mobile telephone exchange or the long transmission connections to the exchange, a lower price can be set for it. If the base station controller in question is located in a company's telephone exchange and its base stations cover the premises of the company, the method can be used to form a similar wireless local area network as the one described above in conjunction with EP document no. 599,632.
So-called, cordless systems, in which the fixed terminals of the conventional wired telephone network are replaced with corresponding radio-based devices, constitute a field of technology of its own. These systems have so far concentrated on standardizing the radio interface between the mobile terminal and the fixed station at the end of a wired connection. Known radio interface standards include, for example, DECT (Digital European Cordless Telecommunications) and CT2 (Cordless Telephone 2). They do not define the communication services offered to the user, but the services depend on the communication network (e.g. the public wired telephone network) to which the fixed station implementing the radio inter-face is connected.
Above solutions according to the prior art do not actually attempt to solve the aforementioned problem caused by the overlapping of networks required by different transmission formats. An object of this invention is to provide a system which combines all electrical communication within a given limited area and controls the communication directed out of said area and provides a chance to share data and data processing resources between several users. Another object of the invention is to provide an arrangement with which said communication-combining system can also serve home and small office users. A further object of the invention is to provide an arrangement like the one mentioned above in which the same equipment can be used everywhere as terminals of the communication system.